Backup Exec cannot connect to the remote agent because a valid trust does not exist between the remote agent and the Backup Exec server. To establish a trust, add the remote computer to the list of servers on the Backup and Restore tab. On the Backup and Restore tab, in the Servers group, click Add.
It does not help to only post an error message without any details of what steps you were following.
Are you trying to restore to same or other Exchange Server?
Are you aware that BE 2012 is no longer supported?